A scanning electron microscope (SEM) capable of performing nanometer-level observation is used in various fields such as a field of semiconductors, a field of materials and a field of biotechnology. The SEM is configured by including an electron source for generating electrons, and an electromagnetic lens for focusing generated electrons onto a sample, and the quality of a SEM image largely depends on performances of these components. For example, the quantity of electrons generated from the electron source, namely, the luminance of the electron source affects the SN (Signal-to-Noise) ratio of the SEM image, and the performance of the electromagnetic lens affects spatial resolution of the SEM image to be obtained.
Patent Literature 1 discloses a technique in which high-energy electrons are emitted from the electron source, and the speed of the high-energy electrons is reduced between an objective lens and a sample, thereby increasing the luminance of the electron source and suppressing the effects from the outside.
Patent literature 2 discloses a technique in which the speed of high energy electrons is reduced on an undersurface of an objective lens, thereby realizing high spatial resolution even when low-energy electrons are emitted to a sample.
Patent Literature 3 discloses an arrangement of a device for accelerating electrons from a first energy to a higher second energy within a range of an intermediate image so as to obtain high point resolution even when beam energy is low.